1. Field of the Invention
The present invention relates to novel total elbow arthroplasty systems. In particular, the present invention is directed to total elbow implants, bone cutting guides for the installation of the implants, and methods for total elbow replacement. The apparatus and methods of the present invention are useful in the treatment of elbow osteoarthritis in canines, as well as in other species, including other quadrupeds and humans.
2. Description of the Background
Elbow osteoarthritis is the most common orthopedic problem of the front leg encountered by the small animal practitioner and veterinary surgeon. (Johnson J. A., et al., V.C.O.T. 7:56-69, 1994.) The etiology of elbow osteoarthritis (OA) is multifactorial, involving developmental conditions such as fragmentation of the medial coronoid process, osteochondrosis, asynchronous growth between the radius and ulna, ununited anconeal process, trauma and idiopathic causes. (Johnson J. A., et al., V.C.O.T. 7:56-69, 1994; Huibregtse B. A., et al., JAAHA 30:190-5, 1994.) The disease is frequently complicated by an early age of onset and patients that are bilaterally affected. (Huibregtse B. A., et al., JAAHA 30:190-5, 1994.) Medical (nonsteroidal antiinflammatories and polysulfated glycosaminoglycans) and/or surgical management of these conditions frequently leads to unsatisfactory results. Huibregtse et al. provide evidence that less than 50% of dogs treated medically and less than 60% of those treated surgically for fragmentation of the medial coronoid process had long-term successful recoveries. (Huibregtse B. A., et al., JAAHA 30:190-5, 1994.) Bouck et al. provided more objective data using force plate gait analysis and documented that lameness did not significantly improve from pretreatment status following medical or surgical therapy. (Bouck G. R., et al., V.C.O.T. 8:177-83, 1995.) Currently, no reliable alternative exists as a means to treat cases that have had unsatisfactory outcomes following medical or surgical management. In fact, none of the current methods of therapy are reliable as a primary therapy for elbow OA.
Improvements in implant designs and surgical techniques have made total elbow arthroplasty a satisfactory treatment for arthritic disorders of the elbow in man. (Kraay M. J., et al., J Bone Joint Surg [Br] 76-b:636-40, 1994.) In two separate evaluations, 91% of total elbow arthroplasty cases had long-term excellent outcomes. (Morrey, B. F., et al., J Bone Joint Surg [Br] 77-B:67-72, 1995.) (Morrey B. F., et al., J Bone Joint Surg [Am] 74-A:479-90, 1992.) Total elbow arthroplasty has been successfully used in man in cases of inflammatory arthritis, osteoarthritis, humeral nonunion and erosive arthritis. (Kraay M. J., et al., J Bone Joint Surg [Br] 76-b:636-40, 1994.) (Morrey, B. F., et al., J Bone Joint Surg [Br] 77-B:67-72, 1995.) (Morrey B. F., et al., J Bone Joint Surg [Am] 74-A:479-90, 1992.)
Although a reliable canine total elbow replacement has not previously been available, total joint arthroplasty has been used in the hind limb of dogs. Specifically, total hip arthroplasty for OA is used in dogs with much success; 95% of dogs have a satisfactory outcome following total hip replacement. Canine total hip arthroplasty has been a multimillion dollar business in the U.S., Europe, and Japan for the last decade. Veterinarians and pet owners accept total joint replacement technology and the cost necessary to make it effective in the dog. The need for canine total elbow arthroplasty parallels that of canine total hip arthroplasty. In addition, many advances in human total knee arthroplasty are linked to successful research using canine models. (Sumner D. R., et al., J Biomechanics 27:929-39, 1994.)
In designing an elbow replacement, there are a number of special considerations. These include the fact that the elbow, unlike the hip or knee, is a three bone system requiring a three implant system or alteration of the existing bony structure. Left and right elbows are mirror images of each other; they are not isometric.
Technology and designs available for human total elbow arthroplasty, although helpful, cannot be directly applied to dogs because of significant anatomical and economical differences. Dogs are quadrupeds and their forelimbs are weight bearing; current total elbow implants used in humans are not designed to withstand the cyclic loading that would occur if used in a dog. In addition, canine bones have more contour than human bones and have increased variability in size and shape making cutting guides based upon the long axis of a bone difficult to use.
Total elbow arthroplasty in the dog is not commercially available, and has not been successfully attempted in the dog. A research group at the University of California at Davis led by Dr. Philip B. Vasseur devised a canine total elbow replacement system in 1995. The elbow replacement system was not studied in vivo before use in three client-owned dogs with naturally occurring elbow arthritis.
The system designed by Vasseur's group used three components, a humeral, a radial, and an ulnar component. The ulnar and humeral components articulated in a semiconstrained fashion. In effect, this means that the ulnar component loosely fit into the humeral component. The radial component articulated with both the humeral and ulnar components in an unconstrained manner. All three implants were designed and used for cemented fixation. All three components were non-isometric, or designed specifically for use in either the left or right limb.
Each of the three cases had an unsatisfactory result following total joint replacement because of implant failure. The research project was terminated (Personal communication with Dr. Vasseur on 10/96.) Malarticulation and loosening of the components led to decreased range of motion, inflammation and joint pain.
Another veterinary practitioner located in Lakeport, Calif., Ralph Lewis, has also designed and performed total elbow arthroplasty. The Lewis system is a constrained or hinged system which includes a humeral component, radioulnar component, a wrist pin screw and a locking screw. In order to install the implant, an osteotomy of the lateral epicondyle of the humerus and the proximal ulna are necessary. These osteotomies require repair with bone plates after the implants are installed.
In addition to requiring removal of a substantial amount of bone and subsequent bone repair, this system is also undesirable because the components are fully constrained (i.e., hinged). When constrained systems are loaded, the majority of the stress is shifted to the implant-cement or implant-bone interface. Constrained systems typically loosen at these stressed interfaces and thus have a much shorter lifespan than unconstrained or semiconstrained systems. Not only does this lead to implant failure, but it also makes FDA approval substantially more difficult to obtain.
Currently there is no total elbow arthroplasty system that satisfactorily manages difficult cases of canine elbow osteoarthritis. There is there fore a need for a canine total elbow replacement that provides a pain free joint which approximates normal range of motion.